A movement at high frequency in at least one axis is necessary to build up an image with the aid of line-by-line writing of a projection area (“flying spot”). Exclusively resonant oscillating arrangements come into consideration to achieve the required frequencies greater than 10 kHz up to 50 kHz. A great variety of micromirrors have been provided in recent years. In part, mirrors have been implemented which oscillate only in one axis; in part, gimbal-mounted mirrors have been developed, which either perform resonant oscillations in both axial directions, or operate quasi-statically in one direction.
The significance of the product of mirror size and deflection, the so-called theta-D product, and the frequency for the image quality of a microscanner are described in MEMS Scanners for Display and Imaging Applications, Proc. of SPIE, volume 5604.
In addition to the three parameters mirror size, deflection, and frequency, the mirror deformation of a micrometer oscillating at high frequencies may amount only to approximately 1/10 of the wavelength of the laser light used. In the event of a greater deformation, the spot would be widened, which worsens the resolution of the image. Because of the inertia of the mirror itself and the counterforces acting on the mirror plate, as are exerted by the springs tensioned upon deflection of the mirror, this is a requirement which is very difficult to meet. By optimizing the suspension points, attempts have previously been made to optimize the deformation by intrinsic inertia of the plate and to optimize the deformation by the spring engagement with respect to a preferably small dynamic deformation of the mirror plate.
In general, a metallization preferably made of silver or aluminum is used for the reflective surface of micromirrors. The carrier of a micromirror is made of silicon, for example. The entire mirror plate therefore represents a bimetal. This results in temperature-dependent static deformation of the mirror.